1. Field of the Invention
The present invention relates to a refrigeration and air conditioning system. In particular, the invention relates to a method and apparatus for saving energy in the operation of a large building employing chilled water air conditioning systems.
2. Description of the Related Art
Both compression and absorption systems are used in chilled water air conditioning systems to cool large buildings. These two air conditioning systems generally use the same design of condenser and evaporator. See the Standard Handbook for Mechanical Engineers, Seventh Edition, Theodore Baumeister, Editor, McGraw-Hill Book Company, New York, N.Y. page 18-12, which is hereby incorporated by reference.
In large buildings, air conditioning systems are designed to promote year-round cooling. This characteristic is essential to a cooling system designed for buildings in which the outer peripheral surfaces and areas are subject to wide temperature gradients while the inner portions remain relatively stable regardless of the ambient conditions.
Such an air conditioning system must, in general, be operated during substantially the entire year to provide the necessary cooling and air circulation. In the winter, the rooms on the outer periphery of the building must be heated and the interior rooms having no external exposure must be cooled. In the summer, the entire building must be cooled.
An air conditioning system utilizing chilled water as the cooling medium circulating between the refrigeration units (chillers) and the rooms or other areas in the building to be cooled is designed with sufficient capacity to cool the building while fully occupied to a comfortable temperature when the ambient air outside the building reaches a preselected maximum temperature. Thus, a chilled water air conditioning system has an excess of cooling capacity even when the building is fully occupied except on days when the outside conditions are at or above the maximum design conditions. Also, as known to those skilled in the art, it is common for a building to have sufficient air conditioning capacity to exceed maximum design conditions. In general, the only time maximum design conditions will be encountered is when the chilled water air conditioning system is restarted after problems have caused the air conditioning system to be shut down on a hot day for a period of time sufficient for the temperature of the interior of the building to rise close to ambient temperatures outside the building.
Most chilled water air conditioning systems are designed to produce a constant flow (gallons per minute) of chilled water. When multiple chillers are employed, and maximum capacity is not required, one or both chillers are commonly operated at less than full capacity. As is known to those skilled in the art, the efficiency of most chillers operating at less than full capacity is reduced, and the energy consumed per ton of cooling is increased.